The present invention relates to brake shoes or liners utilized in an arresting or braking device to control the contact stress imparted into the axially moving ram or plunger to arrest its motion. The arrestor device is provided for the stopping or braking of a ram, plunger or elevator jack in case of undesired downward motion. The arrestor has a pair of arms tiltable by means of a hydro-mechanical system, and the shoes or liners affix to the arms such that they are not touching the ram or cylinder in the open position and engage circumferentially when the arms are in the closed or set position.
In the U.S. Pat. No. 5,810,119, there is shown an arresting device for a hydraulic elevator in which the advantages of the shoes or liners are listed therein. In the present invention, the shoes or liners reflect an improvement of the stopping or arresting ability of the arresting device with a reduced stress inserted into the ram, plunger or jack. This is advantageous as the reduced stress assures that yielding stresses are not imparted into the ram, plunger or jack. Further, the unique characteristics of the present embodiment shoe or liner design, by the grooves and segmentation described herein, provide effective stopping over a wide range of material tensile strengths. It is possible that rams, plungers or jacks can be of varying tensile strengths measured by Rockwell or Brinell methods, converted from hardness to tensile strength and be applied in an elevator application without detriment to the elevator operation or safety. Because of these varying tensile strengths, it was necessary to improve the prior art to accommodate the tensile strength differences and the present embodiment of shoes or liners have shown 100 percent effectiveness over the tensile strength ranges of known rams, plungers or jacks.
The present invention relates to improvements to the shoe or liner by machining and curving or bending the shoes or liners that mount on the arms of an arresting device. The arms pivot about a ram, plunger or jack and when in the open position, allow bi-directional axial motion. In the event of an uncontrolled or undesirable motion in one direction, the arms rotate in unison toward the ram, plunger or jack such that the shoes or liners come into circumferential mechanical contact with the ram causing an arrest of the undesirable axial motion without permanent yielding of the ram, plunger or jack. This device is described in the U.S. Pat. No. 5,810,119.
The preferred embodiment and present invention concerns the machining and shape of the shoes or liners. In practical application it was found that rams, plungers or jacks have various tensile strengths and that allowed the possibility of permanent yielding of the ram, plunger or jack when the arresting stress was applied into rams, plungers or jacks of lower tensile strength steel. After determining the cause of unexpected yielding, the preferred embodiment shoe or liner was designed, tested and found to satisfactorily arrest the low tensile strength rams, plungers or jacks without the permanent yielding seen with the shoe or liner design of the prior art. It has also been successfully tested for effectiveness at higher tensile strengths.
The embodiment of the vertical grooves machined into the shoe or liner material and subsequent segmentation caused by curving the shoe or liner after the machining creates a geometry where the arresting stress is inserted into the ram, plunger or jack at generally uniform, specific locations. This is an improvement over the prior art as the prior art shoes or liners inserted stresses that were more random, given their reliance on circularity of all of the components and consistent wall thickness.
Further, this is an improvement over the prior art as the prior art shoes or liners inserted arresting stress into a population of rams, plungers or jacks that had varying wall thicknesses that caused inconsistent arresting results. Present improvements allow for a uniform compensation for varying wall thicknesses of the ram, plunger or jack by utilizing a spring effect of the shoe or insert material that is formed by a chord formed when the shoe or liner is mounted into its round mounting support and the segment ends under the vertical machining contact the mounting support. This segmentation allows for higher arresting stresses to be compensated for by the spring bending rather than unequally forced back into the ram, plunger or jack. Segmentation around the full circumference therefore allows an equal distribution of stresses allowing ram, plunger or jack yielding stresses to be taken up by the spring effect of the shoe or liner segments.
The improvements also cause a uniform compressive stress load into the ram, plunger or jack wall that adds structural stiffness to the ram plunger or jack material when the arresting stress is applied by the segmented shoes or liners. This arresting stress is also lower with the improved embodiment, that is to say the arresting stress applied with the same loads and ram, plunger or jack is higher with the prior art shoes or liners. This reduces the overall arresting stress that possibly leads to yielding the ram plunger or jack yet retains the satisfactory arrest. This lower arresting stress is a function of the uniform insertion of the stress into the ram, plunger or jack in combination with the spring effect of the segmentation.
Another improvement of the present design overcomes another property of some rams, plungers or jacks, that of a very low coefficient of friction due to the surfacing of the ram, plunger, or jack. By adding friction material such as grit or silica into the improved shoe or liner in a mechanical cavity, a controlled amount of frictional material compensates for the low friction of the ram, plunger or jack and assures proper seating of the arms into their fully arresting position.